GT, you really ought to visit this website for anything SBF.  Bob, there, is extremely knowledgeable on all the combinations and permutations of the breed.

http://www.network54.com/Forum/119417

At 54.5 cc for origional 289 Combustion chambers. Ya using different pistons??. What CR are you expecting to be running??

Tubo

The 58cc AFR heads will give right at 10:1 on a 302 (5.0) with .030 overbore and flat pistons.  So.....at 54.5cc those 289 heads will certainly give higher than 10:1 which might be a bit much for iron heads  The aluminum heads handle it ok but the iron heads may have a tendency to detonate  (ping, knock, dingle) which isn't good.  If you have the dished pistons from the "standard", non HO 5.0, you'll probably be okay.

BB
 

Last edited by Bullet Bob (12/05/2017 7:43 AM)

The tighter LSA has more overlap, so it bleeds off compression at low speeds.  Same idea as using a high stall converter.  The converter is slipping during low RPM, where the load of a locked converter would cause detonation. 

Keep in mind that deck height and gasket selection will also make a difference in compression.  Personally I like to zero deck a block and run a gasket with a 0.040" compressed thickness.  That nets perfect quench distance and a very efficient engine.  But, without disassembling the bottom end there's no way to deck the block, so the alternative is to measure deck height and get a gasket with the right compressed thickness so that the deck height plus the gasket thickness equals 0.040". 

I would say that for a carbed street engine 10:1 with iron heads is too much.  I consider 9.5:1 the limit.  You get one tank of bad gas and its rattle time at 10:1.  With EFI you could run 10:1, or with aluminum heads.  10.5:1 I'd consider the limit for a carb and aluminum heads.  Aluminum heads are good for 1 point more compression in any scenario.  With good tuning you could go 11:1 or even higher with EFI and aluminum heads.  Newer high performance engines are actually exceeding 11:1 because the EFI systems are so good and the heads are so efficient. 

Last edited by TKOPerformance (12/06/2017 12:30 PM)

Another issue with the 289 heads on a roller block. You must put the tappets in before you install the heads. You can not either install or remove them with those heads on.

I'm running a GT40P motor in my 66. The GT40P head has a chamber of 60 CC and put CR right around 9.5:1. I run the cheapest 87 I can find with zero pinging. The P head has a very efficient combustion chamber and needs no more then 30* total timing. This cuts down on pumping losses as well as chances to ping. I have my initial set at 10* BTDC. The P heads also breath much better then the 289 heads. I run a 91 Mustang 5.0 cam, same as your motor, with Cobra 1.72 rockers. Let me tell you, this is a very nice running set up! It pulls hard and loves to rev. It'll pull much harder and faster then the 289 heads will. I was talking with a shop that runs a chassis dump, the guy said this set up is worth around the 250/270 FWHP.

I used off the shelf MAC long tubes with these heads in my 66. Plus all the parts are factory no special pushrods, rockers or AIR ports to block off. I'm very happy with my set up!